The Qur’an describes sin as rust forming on the heart (83:14)

In Qur’an 83:14 Allah says that what people used to do has “rusted over their hearts.” Classical scholars explain this as sins gradually covering the heart until it stops responding to truth.

The Prophet ﷺ also described a black spot forming on the heart when a person sins, which grows if the person continues.

I find this description very powerful because it explains how moral numbness develops gradually rather than suddenly.

How have scholars historically interpreted the concept of rān in this verse?